1. Field of the Invention
The present invention relates to a numerical control system using a special purpose computer of a built-in program type in order to perform a numerical control function, and more particularly to a motor control method and an apparatus therefor in the numerical control system for performing the numerical control function by sharing the same between computers, so that an execution time needed for the numerical control can be shortened.
2. Description of the Prior Art
Generally, the numerical control system mainly performs an automatic control of a machine tool, and more specifically performs chiefly a position set control.
If the numerical control system is applied to an industrial robot, the system controls a transfer of a lathe or a knuckle operation of a robot actuator, which is generally executed by a driving force of an electric motor.
Accordingly, the control on the transfer of the lathe or the knuckle operation of the actuator immediately implies a control of the motor.
The actuator (hereinafter referred to as a control object) travels along several straight lines and curve routes in a three-dimensional coordinate system, and an initial value against the routes thereof is calculated by a computer disposed within the numerical control system when a terminal coordinate of various interpolations and a speed command are given.
The initial value of various interpolations, by way of example, in a linear interpolation, implies a displacement amount per 1 msec generated by rotation of each axis, and the displacement amount corresponds to the number of pulses.
In a circular interpolation, the initial value represents an angle to an end point and the displacement amount rotated by the motor, in other words, the number of pulses.
In other words, if the coordinates and the speed are given, the computer divides the curve appropriately to thereby calculate the initial value by way of a mathematical calculating method.
Accordingly, the initial value of the linear interpolation can be calculated if only two points in a three-dimensional space are designated. The initial value of the circular interpolation can be derived by a designation of 3 points but the routes are calculated by an application of the circular interpolation in the case of a free curve interpolation.
For example, this kind of control apparatus has been presented in a Japanese laid-open Utility Model publication Showa 61-84906.
FIG. 1 is a block diagram for illustrating one embodiment of the conventional control apparatus, the apparatus comprising: a motor control computer 102 for executing a robotic system control; and an administration computer 101 for providing a control change command to the motor control computer (hereinafter referred to as a control computer) by monitoring at all times surrounding changes of an object operated by the robotic system and an apparatus therefor when an operational change is required.
The administration computer 101 transmits a coordinate of the end point and a speed command to the control computer 102 when a command indicative of an interpolation performance is received from a user, and the control computer 102 calculates an initial value corresponding to the interpolation and presently performs an interpolation algorithm.
Servo drivers 103.sub.l -103.sub.n drive the robotic system 104 in accordance with a result of the interpolation algorithm.
However, the motor control method of the conventional numerical control system thus described can not control the motor while the control computer is calculating the initial value, thereby causing a problem in that adaptive control to cope with an instantly changing situation can not be smoothly realized.
Furthermore, there has been a drawback in that the initial value calculation and even various interpolation algorithms are performed in the control computer, thereby increasing a capacity to subsequently call for a large capacity integrated circuits and to naturally increase production cost.